Oxygen bleaching agents continue to be popular in household and personal care products to facilitate stain and soil removal. Bleaches are particularly desirable for their stain-removing, dingy fabric cleanup, whitening and sanitization properties, as well as dye transfer inhibition during and even after the wash and drying process. Oxygen bleaches however are somewhat limited in their effectiveness, because of their extreme temperature rate dependence. Thus, the colder the solution in which they are employed, the less effective the bleaching action. Temperatures in excess of 60° C. are typically required for effectiveness of an oxygen bleaching agent in solution.
For effective bleaching at lower temperatures with hydrogen peroxide, the hydrogen peroxide must be converted into a species having more bleaching activity. One possibility for generating activated peroxy compounds is the use of peracid precursors, so-called “bleach activators” such as TAED and/or NOBS, that are converted by perhydrolysis into the active species.
It is also known to use bleach catalysts to generate activated species, wherein a “bleach catalyst” is understood to be a substance that can improve the bleaching performance of hydrogen peroxide or other peroxygen compounds on a bleachable material without itself participating as a stoichiometric reagent in the reaction. The use of bleach catalysts has the advantage, as compared with the other bleach activation methods, in that sub-stoichiometric quantities of the compound are sufficient, with the result that space and weight can be saved in the formulation of the bleach-containing product. Accordingly, metal bleach catalysts are useful for employment in cleaning compositions utilized for bleaching oxidizable substrates, including stains in solution and on surfaces such as fabric, dishes, countertops, dentures and the like.
However, certain metal bleach catalysts still have shortcomings; for example, they can react too rapidly with hydrogen peroxide, leading to non-productive turnover of available oxygen and reduced bleaching performance. Therefore the pursuit continues for improved metal bleach catalysts, such as those with lower catalyst cost and improved starting material sustainability, as well as better stain selectivity and performance. Accordingly, there is continued interest in identifying and improving metal bleach catalysts.